linux-kernel - Re: [PATCH v2 2/3] bq2415x_charger: Use power

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Message-ID: <CAOf5uwnz6SfeEsbGq62QFgRHJ2ys++VV1+VrULxyR4uH2Z_vJQ@mail.gmail.com>
Date:	Mon, 2 Dec 2013 02:45:06 +0100
From:	Michael Trimarchi <michael@...rulasolutions.com>
To:	Anton Vorontsov <anton@...msg.org>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	freemangordon@....bg, aaro.koskinen@....fi, pavel@....cz
Subject: Re: [PATCH v2 2/3] bq2415x_charger: Use power_supply notifier for automode

Hi

On Mon, Dec 2, 2013 at 1:24 AM, Anton Vorontsov <anton@...msg.org> wrote:
> On Mon, Dec 02, 2013 at 01:02:40AM +0100, Michael Trimarchi wrote:
>> On Sun, Dec 1, 2013 at 11:37 PM, Anton Vorontsov <anton@...msg.org> wrote:
>> > On Mon, Nov 25, 2013 at 08:16:34PM +0100, Michael Trimarchi wrote:
>> > ...
>> >> >> So you can read this value without any type of synchronization
>> >> >> with the power_supply_core
>> >> >> and sysfs implementation?
>> > ...
>> >> https://lists.ubuntu.com/archives/kernel-team/2013-January/025206.html
>> >>
>> >> I found and equivalent scenario that I was trying to said
>> >
>> > That's a good question, actually. Even though in Pali's case the notifier
>> > is atomic (so that we are pretty confident that the object won't be
>> > unregistered), there is still a possiblity of a dead lock, for example. So
>>
>> So if the get_property is a sleeping function it will be a deadlock. Right?
>
> All kind of bad things might happen, yes. But before that I would expect a
> bunch of warnings from might_sleep() stuff.
>
> I would recommend to test the patches using preempt/smp kernels + various
> DEBUG_ kernel options set.
>

Is it more simple to make it not atomic and use a mutex in get_property?

Michael

> Thanks,
>
> Anton
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